The present invention relates to piezoelectric linear motors suitable for use as a driving source in machine tools, precision instruments and other machinery, where both linear positioning accuracy and high push force are essential.
According to the driving mechanism, the existing linear piezoelectric motors can be mainly classified into three categories: the inchworm, the ultrasonic motor and the impact drive mechanism. Generally, these types of piezoelectric motors are used as a linear driving source for precision positioning. Compared with electromagnetic motors, piezoelectric motors have advantages, such as higher positioning accuracy, higher push force, compact size, and no electromagnetic wave is generated.
FIGS. 30(a) to 30(e) show the operation of an inchworm mechanism conventionally proposed as a linear motor. The inchworm mechanism is constructed of a shaft 254 and a tubular traveling body 250 axially movably engaged with the shaft 254. The traveling body 250 is composed of three tubular members (piezoelectric actuators) 251, 252 and 253 which are bonded together at respective axial ends by adhesive or the like. The central tubular member 252 is a piezoelectric actuator capable of axially expanding and contracting, and the opposite tubular member 251 and 253 are piezoelectric actuators capable of radially expanding and contracting. In operation, when the traveling body 250 is intended to be moved rightwardly, for example, as viewed in FIG. 31(a), the left tubular member 251 is radially contracted to grasp the shaft 254 under the condition where the central tubular member 252 is axially contracted and the right tubular member 253 is radially expanded as shown in FIG. 30(b). Then, the central tubular member 252 is axially expanded to thereby rightwardly move the right tubular member 253 (see FIG. 30(c)). Then, the right tubular member 253 is radially contracted to grasp the shaft 254, and the left tubular member 251 is expanded to be loosened (see FIG. 30(d)). Then, the central tubular member 252 is axially contracted to thereby rightwardly move the left tubular member 251 (see FIG. 30(e)). Accordingly, the traveling body 250 can be rightwardly moved by repeating the above operation. In the same principle, the shaft 254 can be also moved by fixing one of the tubular members.
The ultrasonic motor includes a driving member vibrated by the driving source, and the driving member is located in contact with a driven member, so that the vibration of the driving member in a driving direction may be frictionally transmitted to the driven member. The driving member generates a linear vibration of an elliptical vibration as a result of a synthesis of vibrations in two directions perpendicular to each other. Such an ultrasonic motor structurally consists of a vibrating reed type, a traveling wave type, etc.
FIG. 31 shows a typical linear ultrasonic piezoelectric motor constructed of a slider 255, an elastic bar 256, two supports 257 and piezoelectric elements 258. The piezoelectric elements are attached at the ends of the elastic bar 255 supported by member 257. The slider 256 is able to slide along the bar 255. The thrust force of ultrasonic actuators is produced by a traveling wave on the elastic bar 256 and particles at its surface move elliptically. The generation of the traveling wave is made by excitation of piezoelectric elements: two standing waves generate one traveling wave to either direction by combination of the electrical phase shift. The slider 255 in contact with the bar 256 is forced to move through friction force. The intuitive analogy may be xe2x80x9ca surfboard on a wavexe2x80x9d.
FIG. 32 shows a vibrating reed type ultrasonic motor constructed of a piezoelectric vibrator 259 vibrating in its longitudinal direction and a vibrating reed 260 attached to the piezoelectric vibrator 259. The vibrating reed 260 is located in oblique contact with a surface of a driven motor 261, so that the driven member 261 may be driven by the vibrating reed 260 in a given direction.
FIG. 33 shows another ultrasonic linear motor having two legs 262 and 263 driving a rail 264. The legs 262, 263 and a connecting body 265 are vibrating members made of an elastic material such as aluminum. The legs are vibrated by piezoelectric elements 266, 267 mounted at an angle to the leg on one end of each leg. Generally, the phase difference in voltage to be applied to the vibration sources at about 90 degrees, so as to efficiently drive the linear motor. When the vibrating member is vibrated by the vibration source, a standing wave vibration is generated in the entire structure, which results in the generation of elliptical vibration at the free ends of the leg portions. Accordingly, when the free ends of the leg portions are disposed in contact with the driven member (the rail 264), the driving member and driven member move relative to each other.
FIGS. 34(a) to 34(e) show the operational procedure of the impact drive mechanism using piezoelectric elements. Rapid deformation of piezoelectric element is the source of the driving force. The motion mechanism consists of three components: a main object 268, a piezoelectric element 269 and a weigh 270 (see FIG. 34(a)). At first, the main object 268 is stopped. Then, a rapid extension of piezoelectric element 269 is made to generate an impulsive force and it moves the main object 268 against friction (see FIG. 34(b)). Then, the piezoelectric element 269 is contracted slowly so that the reactional force caused by the contraction should not exceed the static friction holding the main object 268 (see FIG. 34(c)). A sudden stop of the contraction may cause another step motion of the main object 268 (see FIG. 34(d)). FIG. 34(e) is the end of the work cycle.
Piezoelectric elements can produce very large push force and very fine displacement resolution. However, there is a common shortcoming for most existing linear piezoelectric motors: the push/holding force is limited by the friction induced at the interface of the stator and the rotor. For inchworm and ultrasonic motors, the motion generated by the piezoelectric elements is transmitted to the rotor by friction. Theoretically, the maximum output push force equals to the maximum static friction at the contact interface between the stator and the rotor. For the impact driving mechanism, the driving force is produced by the impact action induced by the piezoelectric element while the holding force is provided by the static friction as well. In order to transmit the greater push force that is generated by the piezoelectric actuator to the output completely, the self-lock mechanism is applied in this invention to feed and support the actuator and the output parts. In this way the fine displacement produced by the piezo-actuator is transferred to the output step by step.
The present invention provides a piezoelectric electric motor which enables precise positioning to be carried out, provides a self-lock effect, has a small power consumption and a large driving force.
The present invention provides in an exemplary embodiment the above mentioned advantages and other advantages discussed below, amongst other advantages, wherein a linear piezoelectric motor includes a piezoelectric actuator, an actuator container which contains the piezoelectric actuator; an actuator slope which is supported by and slidably actuator slope support, the actuator slope is able to correspond with a surface portion of the actuator container; an output bar which shares a common axis with the actuator and the actuator container and comes in contact with at least one of the actuator and the actuator container on one end of the output bar and an axial load is applied on an opposite end of the output bar; and at least one output slope which is slidably connected to at least one output support.
In another exemplary embodiment a linear piezoelectric motor is provided including a piezoelectric actuator; an actuator container which contains the piezoelectric actuator and holds the piezoelectric actuator; an actuator feeding screw which rotatably engages the actuator container and contacts a feeding support; and an output shaft which shares an axis with the piezoelectric actuator and the actuator container and is subjected to an applied load and rotatably engages an output feeding screw, the output feeding screw contacts an output feeding support.